Process and materials for inducing pre-tilt in liquid crystals and liquid crystal displays

ABSTRACT

A process for inducing pre-tilt in alignment of a liquid crystal medium comprising exposing at least one optical alignment layer, comprising anisotropically absorbing molecules and hydrophobic moieties, to polarized light; the polarized light having a wavelength within the absorption band of said anisotropically absorbing molecules; wherein the exposed anisotropically absorbing molecules induce alignment of the liquid crystal medium at an angle + and -θ with respect to the direction of the polarization of the incident light beam and along the surface of the optical alignment layer, and induce a pre-tilt at an angle Φ with respect to the surface of the optical alignment layer and applying a liquid crystal medium to said optical alignment layer, is described. The invention also is directed to liquid crystal display elements made by the process of the invention and to novel polyimide compositions that are useful as optical alignment layers in the invention.

This invention was made with United States Government support undercooperative agreement No. 70NANB4H1525 awarded by the United StatesDepartment of Commerce. The United States Government has certain rightsin the invention.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 08/624,942 filed Mar. 29,1996 now U.S. Pat No. 5,731,405.

BACKGROUND OF INVENTION

The present invention relates to processes for inducing pre-tilt inalignment of a liquid crystal medium, compositions useful in theseprocesses, and liquid crystal display elements.

Liquid crystal compounds are used in human and machine readabledisplays, finding applications in instrument controls, such as those inmotor vehicles, avionics, medical devices, process control devices andwatches. Display devices are primarily comprised of liquid crystal cellshaving a glass or other substrate coated with a transparent conductivematerial in front and behind a liquid crystal medium. Light transmissionthrough these devices is controlled through orientation of the liquidcrystal compounds or dyes dissolved therein. In this way, a voltage or,in some instances, a magnetic field may be applied to the cell so thatthe liquid crystals are oriented in a fashion such that all, some ornone of the light is passed through. In addition, depending on thedevice geometry, polarizers may be used in conjunction with the liquidcrystal medium to control light transmission.

Aligned liquid crystal cells in commerical use are typically oriented indirections suitable for controlling light transmission. That is, themolecules in the liquid crystal composition are aligned so as to assumea homogeneous or homeotropic alignment. Without external stimuli thedisplay will either appear opaque or transparent. By applying anelectric field the molecules are rotated along a fixed axis so as toalter the transmission properties in a desired fashion.

Current liquid crystal display elements include a product that utilizesa twisted nematic mode, i.e. having a structure wherein the aligningdirection of nematic liquid crystal molecules is twisted by 90° betweena pair of upper and lower electrode substrates, a product utilizing asupertwisted nematic mode, utilizing a birefringent effect, i.e. havinga structure wherein the aligning direction of nematic liquid crystalmolecules is twisted by 180° to 300°, and a product utilizing aferroelectric liquid crystal substance or an antiferroelectric liquidcrystal substance. Common to each of these products is a liquid crystallayer disposed between a pair of substrates coated with a polymericalignment layer. The polymeric alignment layer controls the direction ofalignment of the liquid crystal medium in the absence of an electricfield. Usually the direction of alignment of the liquid crystal mediumis established in a mechanical buffing process wherein the polymer layeris buffed with a cloth or other fiberous material. The liquid crystalmedium contacting the buffed surface typically aligns parallel to themechanical buffing direction. Alternatively, an alignment layercomprising anisotropically absorbing molecules can be exposed topolarized light to align a liquid crystal medium as disclosed in U.S.Pat. Nos. 5,032,009 and 4,974,941, both entitled "Process of Aligningand Realigning Liquid Crystal Media," which are hereby incorporated byreference.

The process for aligning liquid crystal media with polarized light is anoncontact method of alignment which can reduce dust and static chargebuildup on alignment layers. Other advantages of the optical alignmentprocess include high resolution control of alignment direction and highquality of alignment.

Requirements of optical alignment layers for liquid crystal displaysinclude low energy threshold for alignment, transparency to visiblelight (no color), good dielectric properties and voltage holding ratios,long-term thermal and optical stability and in many applications acontrolled uniform pre-tilt angle. Most liquid crystal devices,including displays, have a finite pre-tilt angle, controlled, forinstance, by the mechanical buffing of selected polymeric alignmentlayers. The liquid crystal molecules in contact with such a layer alignsparallel to the buffing direction, but is not exactly parallel to thesubstrate. The liquid crystal molecules are slightly tilted from thesubstrate, for instance by about 2-15 degrees. For optimum performancein most display applications a finite and uniform pre-tilt angle of theliquid crystal is desirable.

The process for aligning liquid crystal media with polarized light hasmany attractive features. However, up to now, controlling the pre-tiltangle of liquid crystals in contact with optical alignment layers, whilemaintaining the uniformity of alignment, has been lacking. Furthermoreto meet the above stated requirements of transparency the use ofanisotropically absorbing molecules that absorb in the visible regionare generally not acceptable.

SUMMARY OF INVENTION

The instant invention provides a process of inducing pre-tilt inalignment of a liquid crystal medium that is useful in aligning liquidcrystal displays and other liquid crystal devices; and new materials foroptical alignment layers that provide excellent alignment propertiesupon exposure to UV light.

Specifically, the present invention provides process for inducingpre-tilt in alignment of a liquid crystal medium adjacent to a surfaceof an optical alignment layer comprising:

(a) exposing at least one optical alignment layer, comprisinganisotropically absorbing molecules and hydrophobic moieties, topolarized light; the polarized light having a wavelength within theabsorption band of said anisotropically absorbing molecules; wherein theexposed anisotropically absorbing molecules induce alignment of theliquid crystal medium at an angle + and -θ with respect to the directionof the polarization of the incident light beam and along the surface ofthe optical alignment layer, and induce a pre-tilt at an angle Φ withrespect to the surface of the optical alignment layer; and

(b) applying a liquid crystal medium to the optical alignment layer.

The invention further pertains to a liquid crystal display elementderived from the process of the invention.

The invention further encompasses novel polyimide compositions forgenerating pre-tilt in alignment of a liquid crystal medium comprising acopolyimide derived from at least one diaryl ketone tetracarboxylicdianhydride, at least one hydrophobic diamine and at least one alicyclictetracarboxylic anhydride, which comprises at least two structuralelements of the formulas IV and V ##STR1## wherein Y is a divalentradical selected from the formulas II and III ##STR2## wherein Z isindependently selected from the group consisting of --S--, --O--, --SO₂--, --CH₂ --,--C(CF₃)₂ --, --C(O)--, --CH₂ CH₂ --, --NR-- and a covalentbond wherein R is a C₁ -C₄ hydrocarbon chain; X is independentlyselected from R₁, --O--R₁, --S--R₁,--N(R₂)--R₁ ; wherein R₁ isindependently selected from C₄ -C₂₀ perfluorinated alkyl chain, C₄ -C₂₀partially fluorinated alkyl chain, and C₁₀ -C₂₀ hydrocarbon chain; X₁ isindependently selected from X and H; R₂ is selected, independently, fromH, C₁ -C₉ hydrocarbon chain and and R₁ ; X₂ is independently selectedfrom the group consisting of H, CL, F, Br, R₃ and R₃ O--, wherein R₃ isindependently selected from the group consisting of C₁ -C₃perflourinated alkyl chain, C₁ -C₃ partially flourinated alkyl chain andC₁ -C₈ hydrocarbon chain; m is 1 or 0; and P is a tetravalent organicradical derived from the alicyclic tetracarboxylic dianhydridecontaining at least four carbon atoms, no more than one carbonyl groupof the dianhydride being attached to any one carbon atom of thetetravalent radical.

The invention further encompasses other novel polyimide compositions forgenerating pre-tilt in alignment of a liquid crystal medium.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a general liquid crystal displaycell of the present invention.

FIG. 2 illustrates pre-tilt angle Φ.

FIG. 3 shows the system used to expose coated substrates to ultravioletlight.

FIG. 4 is a schematic illustration of the system used to expose coatedsubstrates with ultraviolet light from a UV lamp source.

DETAILED DESCRIPTION

As used herein "substrate" means the supporting structure for analignment layer. A substrate can be any solid combination of layeredmaterials that provide a useful function for the final optical alignmentlayer or liquid crystal display. For example, the substrate can be anycombination of the following materials: crystalline or amorphoussilicon, glass, plastic, including polyester, polyethylene andpolyimide; quartz, indium-tin-oxide, gold, silver, silicon dioxide,polyimide, silicon monoxide, anti-reflective coatings, color filterlayers, polarizers and phase compensating films. In practice, some ofthese materials are deposited or coated onto a basic supportingstructure such as glass or plastic.

As used herein, the term "alignment layer" means the layer of materialon the surface of a substrate that controls the alignment of a liquidcrystal layer in the absence of an external field. A "conventionalalignment layer" herein refers to an alignment layer that will onlyalign a liquid crystal layer via processing other than optical means.For example, mechanically buffed polyimides, evaporated silicon dioxide,Langmuir-Blodgett films, have all been shown to align liquid crystals.

As used herein, the term "alignment of liquid crystals" means that thelong molecular axes of the liquid crystal molecules have a preferredlocal alignment direction, or director. The director is the averagedirection of an ensemble of liquid crystal molecules which can bequantified by order parameter or other measurements well known in theart. Orientational order parameters are routinely described by theequation:

    S=1/2<3 cos .sup.2 α-1>

where α is the angle between the director and the long axis of eachmolecule, the molecules being regarded as cylindrically symmetric. Thebrackets denote an average over the ensemble of molecules. Orderparameters range from 0 to 1.0. A 0 value indicates no long rangealignment of the liquid crystals is present. A value of 1.0 indicatesthe liquid crystal molecules are fully aligned along a director.Preferred order parameters resulting from the process of the instantinvention are in the range of about from 0.1 to 1.0.

"Optical alignment layer" herein refers to an alignment layer thatcontains anisotropically absorbing molecules that will align liquidcrystals after exposure with polarized light. Optical alignment layersmay be processed by conventional means, such as mechanical rubbing,prior to or after exposure to polarized light. The anisotropicallyabsorbing molecules of the optical alignment layers exhibit absorptionproperties with different values when measured along axes in differentdirections. The anisotropic absorbing molecules exhibit absorption ofabout from 150 nm to 2000 nm. The anisotropically absorbing molecules ofthe optical alignment layer can be covalently bonded within a main chainpolymer, they can be covalently bonded as side groups to a main polymerchain, they can be present as nonbonded solutes in a polymer, or theycan be in the adjacent liquid crystal layer as a solute and adsorbed onthe surface of a normal alignment layer to give an optical alignmentlayer.

Preferred optical alignment layers have absorbance maxima of about from150 to 1600 nm. More preferable optical alignment layers have absorbancemaxima of about from 150 nm to 800 nm. Most preferable optical alignmentlayers for the present invention have absorbance maxima between 150 and400 nm and especially between 300 and 400 nm.

Anisotropically absorbing molecules useful in preparation of opticalalignment layers are the dichroic arylazo, di(arylazo), tri(arylazo),tetra(arylazo), penta(arylazo), anthraquinone, mericyanine, methine,2-phenylazothiazole, 2-phenylazobenzthiazole, stilbene,1,4-bis(2-phenylethenyl)benzene, 4,4'-bis(arylazo)stilbenes, peryleneand 4,8-diamino-1,5-napthoquinone dyes. Other useful anisotropicallyabsorbing materials are the liquid crystal coupled dichroic dyesdescribed in U.S. Pat. No. 5,389,285.

Preparation of the anisotropically absorbing materials listed above arewell known as shown, e.g., by Huffman et al, in U.S. Pat. No. 4,565,424,Jones et al, in U.S. Pat. No. 4,401,369, Cole, Jr. et al. in U.S. Pat.No. 4,122,027, Etzbach et al, in U.S. Pat. No. 4,667,020, and Shannon etal, in U.S. Pat No. 5,389,285.

Other anisotropically absorbing molecules useful in the preparation ofcolorless optical alignment layers are diaryl ketones having a ketonemoiety or ketone derivative in conjugation with two aromatic rings.Specific families of these molecules useful in optical alignment layersare substituted benzophenones, benzophenone imines, phenylhydrazones,and semicarbazones. Specific benzophenone derivatives preferred inoptical alignment layers for the process of this invention arebenzophenone, 4,4'-diaminobenzophenone,4,4'-bis(trifluoromethyl)benzophenone,3,4'-bis(trifluoromethyl)benzophenone, and3,3'-bis(trifluoromethyl)benzophenone. The benzophenone and4,4'-trifluoromethylbenzophenone imines derived from n-octadecylamine,4-hexyloxyaniline and 4-octadecyloxyaniline are also preferred. Thephenylhydrazones of benzophenone, 4,4'-bis(trifluoromethyl)benzophenone,3,4'-bis(trifluoromethyl)benzophenone,3,3'-bis(trifluoromethyl)benzophenone, derived from condensation withphenylhydrazine; and the 2,4-diaminophenylhydrazones of benzophenone,4,4'-bis(trifluoromethyl)benzophenone,3,4'-bis(trifluoromethyl)benzophenone, and3,3'-bis(trifluoromethyl)benzophenone, derived from the chemicalreduction of the corresponding 2,4-dinitrophenylhydrazones are alsopreferred in optical alignment layers for the present invention.

Preferred anisotropically absorbing molecules for optical alignmentlayers are arylazo, poly(arylazo), stilbene and diaryl ketonederivatives. Arylazo, stilbene and diaryl ketone derivatives are themost preferred dyes for optical alignment layers having absorbancemaxima of about from 150 to 400 nm. Poly(arylazo) dyes are mostpreferred for optical alignment layers having absorbance maxima of aboutfrom 400 to 800 nm. A most preferred poly(azo) dye is diazodiamine A; amost preferred stilbene dye is 4,4'-diaminostilbene, B; a most preferredarylazo dye is monoazodiamine C (Table 1). The preparation of the dye Ais described in U.S. Pat. No. 5,389,285; synthesis of dye C is describedin the examples; and 4,4'-diaminostilbene is commercially available fromAldrich Chemical Co., Milwaukee, Wis., as the dihydrochloride salt.

Diaryl ketone tetracarboxylic dianhydrides are especially useful andpreferred as anisotropically absorbing molecules. Preferred diarylketone tetracarboxylic dianhydrides are further described in greaterdetail infra in the discussion of polyimides.

Optical alignment layers used in the process of this invention alsocomprise hydrophobic moieties. "Hydrophobic moieties" refer tofunctional groups that impart strong water imicibility and high surfacetension properties to materials. The hydrophobic moieties are usually,but not exclusively, covalently bonded to a polymer that also acts as amatrix or carrier for the anisotropically absorbing molecules that makeup the optical alignment layer. Most notable hydrophobic moieties arefluorinated and partially fluorinated alkyl chains and long chainaliphatic hydrocarbons. Common hydrophobic moieties containingfluorinated and partially fluorinated alkyl chains, for instance, aremonovalent 1H, 1H-pentadecafluoro-1-octyloxy and11H-eicosafluoroundecanoyl groups, which are readily available fromcommercial materials or well known syntheses. Common hydrophobescontaining long aliphatic hydrocarbon chains are the monovalenthexadecyl, hexadecyloxy, octadecyl, and octadecyloxy groups and thedivalent hexadecylmethylene and octadecylmethylene groups.

Methods for incorporating hydrophobic moieties into many polymermaterials are well known. Examples of polymers having hydrophobicmoieties that are useful as matrices for optical alignment layers arepoly(methyl methacrylate) and poly(methyl acrylate) copolymerscontaining various loadings of fluoroalkyl methacrylates and fluoroalkylacryaltes such as 1H, 1H, 11H,-eicosafluoroundecyl methacrylate, forexample.

Aromatic diamines substituted with hydrophobic moieties are especiallyuseful and preferred as hydrophobic moieties in the synthesis ofpolyimides for optical alignment layers. Preferred hydrophobic diaminesare further described infra in the discussion of polyimides.

Preferably, anisotropically absorbing molecules and hydrophobic moietiesare covalently bonded to polymers. For instance, poly(amic acid)s, whichare precursors to polyimides, can be prepared with anisotropic absorbingmaterials covalently bonded into the poly(amic acid) polymer chain. Thistypically is accomplished by mixing of dianhydride and diamines,including the anisotropically absorbing molecules as one of the tworeactive components. For instance, 4,4'-diaminostilbene is ananisotropically absorbing molecule that also can act as a reactivediamine in polyimide synthesis. 3,3'4,4'-benzophenonetetracarboxylicanhydride is an anisotropically absorbing molecule that also can act asa reactive dianhydride in polyimide synthesis. Allowing the diamines anddianhydrides to polymerize in a solvent such as N-methylpyrolidone ortetrahydrofuran provides a prepolymer solution that is then coated onsubstrates and oven baked to give the final polyimide optical alignmentlayers.

Alternatively, optical alignment layers can have anisotropicallyabsorbing molecules present as nonbonded solutes dissolved in a polymercontaining hydrophobic moieties. These are referred to as guest-hostoptical alignment layers. They are prepared by coating on substrates athin layer of organic material containing the anisotropically absorbingmolecules. Typically the anisotropically absorbing molecules aredissolved in solution along with a polymeric material. The solution isthen coated on substrates using, typically, a spin casting technique.The coatings are then oven baked to remove residual solvent and performthe final cure.

Alternatively, optical alignment layers are prepared by coatingconventional alignment layers such as a hydrophobic polyimide on thesubstrates. The anisotropically absorbing molecules are dissolved in aliquid crystal medium to give a guest-host mixture. When the guest-hostmixture containing anisotropically absorbing molecules is allowed tocontact a conventional alignment layer an optical alignment layer isformed.

Alternatively, optical alignment layers are prepared by coatingconventional alignment layers such as hydrophobic polyimide on thesubstrates and anisotropically absorbing molecules are dissolved in asolvent. When the solution containing anisotropically absorbingmolecules is coated on the conventional alignment layer an opticalalignment layer is formed.

Preferred polymers for optical alignment layers of this invention arepolyimide polymers. The preparation of polyimides is described in"Polyimides", D. Wilson, H. D. Stenzenberger, and P. M. HergenrotherEds., Chapman and Hall, New York (1990). Typically polyimides areprepared by the condensation of one equivalent of a diamine componentwith one equivalent of a dianhydride component in a polar solvent togive a poly(amic acid) prepolymer intermediate. Typical solvents used inthe condensation reaction are N-methyl-pyrrolidone (NMP),dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide(DMSO), butyl cellosolve, ethylcarbitol, γ-butyrolactone, etc. Thepoly(amic acid) is typically formulated to give a 1 to 30 wt % solution.The condensation reaction is usually performed between room temperatureand 150° C. The prepolymer solution is coated onto a desired substrateand thermally cured at between 180° and 300° C. to complete theimidization process. Alternatively, the poly(amic acid) prepolymer ischemically imidized by addition of a dehydrating agent to form apolyimide polymer. Examples of chemical imidzation reagents are organicanhydrides such as acetic anhydride and trifluoroacetic anhydride incombination with organic bases such as triethyl amine and pyridine.Other chemical imidization reagents are ethylchloroformate andtriethylamine, thionyl chloride, oxalyl chloride, acetyl chloride anddicyclohexylcarbodiimide. Chemical imidizations are performed betweenroom temperature and 150° C. Chemical imidization requires that theresulting polyimide be soluble in a solvent for further processing.Achieving solubility often requires polyimides to be speciallyformulated for chemical imidization. The chemically imidized polyimidesolution is coated onto a substrate and heated to remove solvent, but nohigh temperature cure is required. Preferred compositions of thisinvention are chemically imidized polyimides.

Especially useful in the process of the invention is a polyimide polymerthat is the condensation reaction product of hydrophobic diamines anddianhydrides. Preferred is a polyimide polymer that is a homopolymide ora copolyimide of at least one tetracarboxylic dianhydride and at leastone hydrophobic diamine, which comprises at least one structural elementof the formula I: ##STR3## wherein Y is a divalent radical selected fromthe formula II and III ##STR4## wherein Z is selected from the groupconsisting of --S--, --O--, --SO₂ --, --CH₂ --,--C(CF₃)₂ --, --C(O)--,--CH₂ CH₂ --, --NR-- and a covalent bond wherein R is a C₁ -C₄hydrocarbon chain; X is independently selected from R₁, --O--R₁,--S--R₁, --N(R₂)--R₁ ; wherein R₁ is independently selected from C₄ -C₂₀perfluorinated alkyl chain, C₄ -C₂₀ partially fluorinated alkyl chain,and C₁₀ -C₂₀ hydrocarbon chain; X₁ is independently selected from X andH; R₂ is independently selected from H, C₁ -C₉ hydrocarbon chain and andR₁ ; and wherein M is a tetravalent organic radical derived from saidtetracarboxylic dianhydride containing at least two carbon atoms, nomore than two carbonyl groups of the dianhydride being attached to anyone carbon atom of the tetravalent radical.

Diamines useful in this invention to induce a finite pre-tilt of aliquid crystal medium as well as provide good alignment uniformity arelisted in Table 2. Preferred hydrophobic diamines have the structure

    NH.sub.2 --Y--NH.sub.2

wherein Y is as described above. Specific hydrophobic diamines that arepreferred in this invention are 4-(1H,1H-pentadecafluoro-1-octyloxy)-1,3-benzenediamine (8) and 4-(1H, 1H,11H-eicosafluoro-1-undecyloxy)-1,3-benzenediamine (9). Specific diamineshaving hydrocarbon chains that are preferred are4-(1-octadecyloxy)-1,3-benzenediamine (10),4-(1-hexadecyl-1,3-benzenediamine and2-(1-octadecyloxy)-1,4-benzenediamine (12).

Specific hydrophobic diamines useful in this invention are readilyavailable by synthesis. The dinitro compounds corresponding to diamines8 and 9 are prepared by nucleophilic displacement of halogen from1-halo-2,4-dinitrobenzenes with 1H, 1H-pentadecafluoro-1-octanol and 1H,1H, 11H-eicosafluoro-1-undecanol, respectively, which are available fromPCR Inbc. (Gainesville, Fla. 32602). They are chemically reduced todiamines to provide the diamines 8 and 9 as described by Ichino, et al,in J. Poly. Sci., 28, 323 (1990). Dinitro compounds corresponding todiamines 10-13 are prepared by alkylation of 2,4-dinitrophenol or 2,5dinitrophenol with alkyl bromides in dimethylformamide/sodium carbonateat 90°-100° C. The dinitro compound corresponding to diamine 14 isprepared by nitration of n-octylbenzene. The dinitro compoundscorresponding to diamines 15 and 16 are prepared from1-chloro-2,4-dinitrobenzene as described in U.S. Pat. No. 4,973,429. Thedinitro compounds are reduced to the corresponding diamines 10-16chemically with tin (II) chloride/ethanol or catalytically with hydrogenand palladium/carbon.

Other diamines that can be used in combination with the hydrophobicdiamines described above can very widely. Specific examples include thetrifluoromethyl substituted diamines 1-7 and the lower hydrocarbonhomologs 11, 13, and 14 of Table 2. Aromatic diamines which can be usedinclude p-phenylenediamine, m-phenylenediamine, 2,5-diaminotoluene,2,6-diaminotoluene, 4,4'-diaminobiphenyl,3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl,diaminodiphenylmethane, diaminodiphenyl ether,2,2-diaminodiphenylpropane, bis(3,5-diethyl-4-aminophenyl)methane,diaminodiphenylsulfone, diaminonaphthalene,1,4-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenyl)benzene,9,10-bis(4-aminophenyl)anthracene, 1,3-bis(4-aminophenoxy)benzene,4,4'-bis(4-aminophenoxy)diphenylsulfone, 2,2-bis4-(4-aminophenoxy)phenyl!propane,2,2-bis(4-aminophenyl)hexafluoropropane and 2,2-bis4-(4-aminophenoxy)phenyl!hexafluoropropane; alicyclic diamines such asbis(4-aminocyclohexyl)methane;and aliphatic diamines such astetramethylenediamine and hexamethylene diamine. Further,diaminosiloxanes such as bis(3-aminopropyl)tetramethyldisiloxane canalso be used. Such diamines may be used alone or in combination as amixture of two or more.

Other diamines that are preferred in the process and polyimidecompositions of the instant invention are diaminobenzophenones.Diaminobenzophenones are diaryl ketones and thus act as another sourceof photoactive species in the process. In copolyimides incorporatingboth diamino and dianhydride derivatives of diaryl ketones, a largerconcentration of active chromophore can be achieved. Preferreddiaminobenzophenones for copolyimide compositions of the instantinvention is 4,4'-diaminobenzophenones and 3,4'-diaminobenzophenone.

Preferrably the hydrophobic diamines comprise about from 1.0 to 50 mol %of the diamine component, and most preferrably the hydrophobic diaminescomprise about from 1.0 to 15 mol % of the diamine component. Loadingsof the hydrophobic diamine greater than about 50 mol % of the diaminecomponent tend to give pre-tilts greater 30 degrees.

In a preferred process of this invention the polyimide polymer is acopolyimide which additionally comprises at least one structural elementof formula Ia ##STR5## wherein Y₁ is a divalent organic radical havingat least two carbon atoms other than Y; M is as described above; andwherein the ratio of structural elements of fromula I and Ia are aboutfrom 1:99 to 99:1.

The tetracarboxylic dianhydrides useful in forming polyimides for theinvention have the structural formula: ##STR6## wherein M is atetravalent organic radical containing at least two carbon atoms, nomore than two carbonyl groups of the dianhydride being attached to anyone carbon atom of the tetravalent radical.

Specific examples of the tetracarboxylic dianhydride component includearomatic dianhydrides such as pyromellitic dianhydride,2,3,6,7-naphthalenetetracarboxylic dianhydride,1,2,5,6-naphthalenetetracarboxylic dianhydride,1,4,5,8-naphthalenetetracarboxylic dianhydride,3,3'4,4'-biphenyltetracarboxylic dianhydride,2,3,2',3'-biphenyltetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride,3,3'4,4'-benzophenonetetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)diphenylsulfone dianhydride,bis(3,4-dicarboxyphenyl)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,1,1,1,3,3,3-hexafluoro-2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride,2,3,4,5-pyridinetetracarboxylic dianhydride; alicyclic tetracarboxylicdianhydrides such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-butanetetracarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride,1,2,4,5-cyclohexanetetracarboxylic dianhydride,2,3,5-tricarboxycyclopentylacetic acid dianhydride and3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride; andtheir acid and acid chloride derivatives.

Diaryl ketone tetracarboxylic dianhydrides especially useful for theinvention are those having the following structure: ##STR7## wherein X₂is independently selected from the group consisting of H, CL, F, Br, R₃and R₃ O, wherein R₃ is independently selected from C₁ -C₃perflourinated alkyl chain, C₁ -C₃ partially flourinated alkyl chain andC₁ -C₈ hydrocarbon chain; m is 1 or 0; and Z is selected from the groupconsisting of --S--, --O--, --SO₂ --, --CH₂ --, --C(CF₃)₂ --, --C(O),--CH₂ CH₂ --, --NR-- and a covalent bond wherein R is a C₁ -C₄hydrocarbon chain. The more preferred diaryl ketones are3,3',4,4'-benzophenonetetracarboxylic dianhydride (D1) and2,2'-dichloro-4,4',5,5'-benzophenone tetracarboxylic dianhydride (D2).The most preferred benzophenone tetracarboxylic dianhydride for thisinvention is 3,3',4,4'-benzophenonetetracarboxylic dianhydride (D1).Other related photosensitive diaryl ketone dianhydrides described byPfeifer, et al., in U.S. Pat. No. 4,698,295, herein incorporated byreference, are useful alternatives to the benzophenonetetracarboxylicdianhydrides in the process of this invention.

Specific benzophenonetetracarboxylic dianhydrides preferred in thisinvention are readily available from commercial sources or synthesis.For instance, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (D1) isavailable from Aldrich Chemical Co., Inc. (1001 W. St. Paul Ave.,Milwaukee, Wis. 53233). 2,2'-Dichloro-4,4',5,5'-benzophenonetetracarboxylic dianhydride (D2) is available from 4-chloro-o-xylene byFriedel-Crafts acylation with oxalyl chloride to give2,2'dichloro-4,4',5,5',-tetramehtylbenzophenone, followed by oxidationwith nitric acid and dehydration of the resulting tetracarboxylic acidas described by Falcigno, et al., J. Poly. Sci. 1992, 30, 1433.

"Alicyclic tetracarboxylic dianhydrides" refer to dianhydrides that arecomprised either partially or in whole of saturated carbocyclic rings.The alicyclic tetracarboxylic dianhydrides impart useful solubilityproperties to polyimides comprising them. Alicyclic tetracarboxylicdianhydrides suitable for the invention are those listed in Table 3.Preferred alicyclic dianhydrides are5-(2,5-dioxotetrahydro)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride (D3), 2,3,5-tricarboxycyclopentaneacetic acid dianhydride(D4), cyclobutanetetracarboxylic acid dianhydride (D5) and1,2,3,4'-butanetetracarboxylic acid dianhydride (D7).

5-(2,5-Dioxotetrahydro)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride (D3) is commercially available from Chriskev Co, Inc.1,2,3,4-Cyclobutanetetracarboxylic acid is available from AldrichChemical Co., Inc. and can be readily converted to the dianhydride withoxalyl chloride. 2,3,5-Tricarboxycyclopentaneacetic acid dianhydride(D4) is available via synthesis by oxidation of dicyclopentadiene withnitric acid as described by Hession, et al., in British Patent 1 518 322(1976). The synthesis of 1,2,3,4-cyclobutanetetracarboxylic dianhydride(D5) is described by Moore, et al, Chem. Mat., 1989, 1, 163.1,2,3,4-butanetetracarboxylic acid dianhydride (D7) is available bytreatment of the corresponding tetracarboxylic acid (Aldrich) withacetic anhydride.5,5'-(1,1,3,3-Tetramethyl-1,3-disiloxanediyl)-bis-(norbornane-2,3-dicarboxylicanhydride) (D9) is available by hydrosilation of5-norbornene-2,3-dicarboxylic anhydride with1,1,3,3-tetramethyldisiloxane as described by Ryang in U.S. Pat. No.4,381,396.

Bicyclo 2.2.1!heptanetetacarboxylic 2,3:5,6-dianhydride (D10) isavailable by synthesis from bicyclo 2.2.1!hept-5-ene-2,3-dicarboxylicanhydride as described by Matsumoto et al., in Macromolecules 1995, 28,5684. Bicyclo 2,2,2!oct-7-enetetracarboxylic 2,3:5,6-dianhydride (D11)is available by synthesis from 4-cyclohexene-1,2-dicarboxylic anhydrideas described by Itamura, et al., in Macromolecules 1993, 26, 3490.

In preparing polyimides for optical alignment layers the molar ratio ofdiamine to dianhydride usually is 1:1, but can vary between 0.8:1 to1:1.2. The preferred ratio of diamine to dianhydride is between 0.98:1and 1:1.02. Most preferred is a 1:1 ratio of diamine to dianhydride.

Another embodiment of this invention is a novel polyimide composition,derived from a diamine component and a dianhydride component, forgenerating pre-tilt in alignment of a liquid crystal medium comprising acopolyimide derived from at least one diaryl ketone tetracarboxylicdianhydride, at least one hydrophobic diamine and at least one alicyclictetracarboxylic anhydride, which comprises at least two structuralelements of the formulas IV and V ##STR8## wherein Y is a divalentradical selected from the formulas II and III ##STR9## wherein Z isselected, independently, from the group consisting of --S--, --O--,--SO₂ --, --CH₂ --, --C(CF₃)₂ --, --C(O)--, --CH₂ CH₂ --, --NR-- and acovalent bond wherein R is a C₁ -C₄ hydrocarbon chain; X isindependently selected from R₁, --O--R₁, --S--R₁,--N(R₂)--R₁ ; whereinR₁ is independently selected from C₄ -C₂₀ perfluorinated alkyl chain, C₄-C₂₀ partially fluorinated alkyl chain, and C₁₀ -C₂₀ hydrocarbon chain;X₁ is independently selected from X and H; R₂ is selected,independently, from H, C₁ -C₉ hydrocarbon chain and and R₁ ; X₂ isindependently selected from the group consisting of H, CL, F, Br, R₃ andR₃ O--, wherein R₃ is independently selected from C₁ -C₃ perflourinatedalkyl chain, C₁ -C₃ partially flourinated alkyl chain and C₁ -C₈hydrocarbon chain; m is 1 or 0; and P is a tetravalent organic radicalderived from said alicyclic tetracarboxylic dianhydride containing atleast four carbon atoms, no more than one carbonyl group of thedianhydride being attached to any one carbon atom of the tetravalentradical. Most preferred is a composition wherein the copolyimidecomprises a ratio of structural elements of formula IV and V of 1:10 to99:1.

Another preferred polyimide composition additionally includes at leastone diaminobenzophenone, additionally comprising at least one structuralelement of formulas VII and VIII ##STR10## wherein Z, X₂, P and m are asdescribed above.

Another embodiment of the invention is a polyimide composition, derivedfrom a diamine component and a dianhydride component, for generatingpre-tilt in alignment of a liquid crystal medium comprising acopolyimide derived from at least one diaryl ketone tetracarboxylicdianhydride, at least one hydrophobic diamine and at least onediaminobenzophenone, which comprises at least two structural elements ofthe formulas IV and VII ##STR11## wherein Y, Z, X, X₁, X₂, and m are aspreviously described.

Another embodiment of the invention is a polyimide composition, derivedfrom a diamine component and a dianhydride component, for generatingpre-tilt in alignment of a liquid crystal medium comprising acopolyimide derived from least one alicyclic tetracarboxylicdianhydride, at least one hydrophobic diamine and at least onediaminobenzophenone, which comprises at least two structural elements ofthe formulas V and VIII ##STR12## wherein Y, Z, X, X₁, X₂, P and m areas previously described.

Another embodiment of the invention is polyimide composition, derivedfrom a diamine component and a dianhydride component, for generatingpre-tilt in alignment of a liquid crystal medium comprising acopolyimide derived from at least one diaryl ketone tetracarboxylicdianhydride, at least one hydrophobic diamine and at least one diaminederived from a radical Y₂, comprising at least one structural element ofthe formulas IV and IVa ##STR13## wherein Y, Z, X, X₁, X₂, P and m areas previously described and Y₂ is a divalent radical selected from theformulas IIa and IIIa ##STR14## wherein X₃ is independently selectedfrom C₁ -C₃ perfluorinated alkyl chain. partially fluorinated alkylchain or --OCF₃ ; and X₄ is independently selected from X₃ and H.

In all the preferred compositions described above there are generalpreferences for certain functionality. A most preferred diaryl ketonetetracarboxylic anhydride is 3,3',4,4'-benzophenonetetracarboxylicdianhydride. Preferred alicyclic tetracarboxylic acid dianhydrides are5-(2,5-dioxotetrahydro)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, 2,3,5-tricarboxycyclopentaneacetic acid dianhydride,1,2,3,4-butanetetracarboxylic acid dianhydride andcyclobutanetetracarboxylic acid dianhydride. Most preferred are5-(2,5-dioxotetrahydro)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, 2,3,5-tricarboxycyclopentaneacetic acid dianhydride and1,2,3,4-butanetetracarboxylic acid dianhydride which give usefulsolubility properties to the polyimides. Most preferred hydrophobicdiamines are selected from the group consisting of 4-(1H,1H-pentadecafluoro-1-octyloxy)-1,3-benzenediamine, 4-(1H, 1H,11H-eicosafluoro-1-undecyloxy)-1,3-benzenediamine,4(1-octadecyloxy)-1,3-benzenediamine, 4-(1-hexadecyl)-1,3-benzenediamineand 2-(1-octadecyloxy)-1,4-benzenediamine. 4,4'-Diaminobenzophenone is amost preferred diaminobenzophenone. Most preferrably radical Y₂ isderived from a diamine selected from the group consisting of2-(trifluoromethyl)-1,4-benzenediamine (1),5-(trifluoromethyl)-1,3-benzenediamine (2),2,2'-bis(trifluoromethyl)benzidene (7),2,2'-bis(trifluoromethoxy)benzidene (6) and3,3'-bis(trifluoromethyl)benzidene (5).

Preferrably the hydrophobic diamines comprise 1.0 to 50 mol % of thediamine component, and most preferrably the hydrophobic diaminescomprise 1.0 to 15 mol % of the diamine component. As will be readilyappreciated by those skilled in the art, there is variation in theperformance among the many embodiments of the present invention. Mostbasically, while the required anistropically absorbing molecules andhydrophobic moieties impart the desired pre-tilt at any concentration,the degree of the effect will be greater with greater concentrations.Similarly, there is a variation in the performance realized betweenspecific anisotrodically absorbing molecules and hydrophobi moieties.For example, among the diamines detailed in Table 2, despite asimilarity in structure, diamine 10 has been found to yield superiorperformance to diamine 12, and diamine 8 has been generally found to beparticularly satisfactory.

The compositions of the invention provide a combination of highsolubility and optical alignment performance (a finite pre-tilt, lowenergy threshold, high quality alignment & transparency to visiblelight) that is very desirable for the fabrication of liquid crystaldisplay elements.

To prepare the optical alignment layers of this invention poly(amicacid) solutions or preimidized polyimide solutions polymer solutions arecoated onto desired substrates. Coating is usually accomplished with 2to 30 wt % solids. Any conventional method may be used to coat thesubstrates including brushing, spraying, spin-csating, dipping orprinting. The coated substrates are heated in an oven under an inertatmosphere, for instance nitrogen or argon, at elevated temperatureusually not exceeding 300° C. and preferrably at or below 180° C. for 1to 12 hours, preferrably for 2 hours or less. The heating processremoves the solvent carrier and may be used to further cure the polymer.For instance, the poly(amic) acid films are thermally cured to generatepolyimide films.

The optical alignment layers are exposed to polarized light to inducealignment of liquid crystals. By "polarized light" we mean light that iselliptically polarized such that the light is more polarized along oneaxis (referred to as the major axis) versus the orthogonal axis(referred to as the minor axis). The preferred polarization is linearlypolarized light where the light is polarized mostly along one axis (themajor axis) with little or no polarization component along the minoraxis. In this invention the polarized light has one or more wavelengthsof about from 150 to 2000 nm and preferably about from 150 to 1600 nmand more preferably about from 150 nm to 800 nm. Most preferably thepolarized light has one or more wavelengths of about from 150 to 400 nmand expecially about from 300 and 400 nm. A preferred source of light isa laser, e.g., an argon, helium neon, or helium cadmium. Other preferredsources of light are mercury arc, xenon lamps, deuterium and quartztungsten halogen lamps, and black lights in combination with apolarizer. Polarizers useful in generating polarized light fromnonpolarized light sources are interference polarizers made fromdielectric stacks, absorptive polarizers and reflective polarizers basedon Brewster reflection. With lower power lasers or when aligning smallalignment regions, it may be necessary to focus the light beam onto theoptical alignment layer.

By "exposing" is meant that polarized light is applied to the entireoptical alignment layer or to a portion thereof. The light can bestationary or rotated. Exposures can be in one step, in bursts, inscanning mode or by other methods. Exposure times vary widely with thematerials used, etc., and can range from less than 1 msec to over anhour. Exposure may be conducted before or after contacting the opticalalignment layer(s) with the liquid crystal medium. Exposing can beaccomplished by linearly polarized light transmitted through at leastone mask having a pattern or with a beam of linearly polarized lightscanned in a pattern. Exposing also may be accomplished usinginterference of coherent optical beams forming patterns, i.e.,alternating dark and bright lines.

Exposure energy requirements vary with the formulation and processing ofthe optical alignment layer prior and during exposure. For example,materials that possess high glass transition temperatures can havehigher energy density requirements for optical alignment. Whereas,material systems designed to have a low glass transition temperatureprior to exposure can have lower energy density requirements. Apreferred range of exposure energy is about from 0.001 to 2000 J/cm².More preferred is the range of about from 0.001 to 100 J/cm² and mostpreferred range of exposure energy is about from 0.001 to 5 J/cm². Lowerexposure energy is most useful in large scale manufacturing of opticalalignment layers and liquid crystal display elements. Lower exposureenergy also minimizes the risk of damage to other materials on thesubstrates.

The efficiency of the alignment process, and the exposure energyrequired, may be further impacted by heating, beyond that inherent inthe "exposing" step. Additional heating during the exposing step may beaccomplished by conduction, convection or radiant heating, or byexposure to unpolarized light. Additional heating may increase themobility of the molecules during exposure and improve the alignmentquality of the optical alignment layer. Additional heating is not arequirement of the process of the invention but may give beneficialresults.

Exposing also can consist of two or more exposure steps wherein theconditions of each step such as angle of incidence, polarization state,energy density, and wavelength are changed. At least one of the stepsmust consist of exposure with linearly polarized light. Exposures canalso be localized to regions much smaller than the substrate size tosizes comparable to the entire substrate size. A preferred method ofdual exposing comprises a two step process of:

(a) exposing at least one optical alignment layer to polarized light ata normal incidence, and

(b) exposing the optical alignment layer to polarized light at anoblique incidence.

Another preferred method of dual exposing comprises a two step processof:

(a) exposing said optical alignment layer to polarized light of a firstdirection of linear polarization of the incident light beam, and

(b) exposing said optical alignment layer to polarized light of a seconddirection of linear polarization of the incident light beam.

Another preferred method of dual exposing comprises a two step processof:

(a) exposing said optical alignment layer to polarized light of a firstdirection of linear polarization of the incident light, and

(b) exposing said optical alignment layer to polarized light of a seconddirection of linear polarization of the incident light, at an obliqueincidence.

As liquid crystal substances used for liquid crystal display elements,nematic liquid crystal substances, ferroelectric liquid crystalsubstances, etc. are usable. Useful liquid crystals for the inventiondescribed herein include those described in U.S. Pat. No. 5,032,009 andnew superfluorinated liquid crystals exemplified by ZLI-5079, ZLI-5080,ZLI-5081, ZLI-5092, ZLI-4792, ZLI-1828, MLC-2016, MLC-2019, MLC-6252,and MLC-6043 available from EM Industries, Hawthorne N.Y. Also usefulare guest-host formulations prepared with all types of liquid crystalsand anisotropically absorbing dyes as described in U.S. Pat. No.5,032,009. Also useful in this invention are nematic and ferroelectricliquid crystals that are disclosed in U.S. Pat. No. 5,447,759 entitled"Liquid Crystal Alignment Film and Liquid Crystal Display Elements,"hereby incorporated by reference.

Chiral dopants are often added to these liquid crystals to induce atwist in one direction, in the liquid crystal medium. Left and righthanded chiral dopants are available. Typical examples are ZL1-811,S-1011 and R-1011, all available from EM Industries.

Other liquid crystals useful in this invention include the polymerizableliquid crystals as described in U.S. Pat. No. 5,073,294; and the liquidcrystal difunctional methacrylate and acrylate monomers as described inU.S. Pat. No. 4,892,392. Both patents are hereby incorporated byreference.

Still other liquid crystals useful in this invention include liquidcrystal polymers as described in U.S. Pat. No. 5,382,548 which is herebyincorporated by reference. These polyester and polyurethane liquidcrystal polymers have low rotational viscosities between their glasstransition (T_(g)) and their isotropic transition (T_(ni)) and readilyrespond to surface aligning forces.

Preferred liquid crystals for the invention are nematic liquid crystals,ferroelectric liquid crystals, polymerizable nematic liquid crystals andnematic liquid crystalline polymers. Especially preferred liquid crystalfor the invention are nematic liquid crystal and polymerizable nematicliquid crystals. Specific families of nematic liquid crystals that arepreferred are the 4-cyano-4'-alkylbiphenyls,4-alkyl-(4'-cyanophenyl)cyclohexanes and the superflourinated liquidcrystal mixtures selected from the group of ZLI-5079, ZLI-5080,ZLI-5081, ZLI-5092, ZLI-4792, ZLI-1828, MLC-2016, MLC-2019, MLC-6252,and MLC-6043 available from EM Industries, Hawthorne N.Y.

Applying a liquid crystal medium to the optical alignment layer can beaccomplished by capillary filling of a cell, by casting of a liquidcrystal medium onto an optical alignment layer, by laminating apreformed liquid crystal film onto an optical alignment layer or byother methods. Preferred methods are capillary filling of a cell andcasting of a liquid crystal medium onto an optical alignment layer.

A cell can be prepared by using two coated substrates to provide asandwiched layer of liquid crystal medium. The pair of substrates canboth contain optical alignment layers or a conventional alignment layer(e.g., mechanically buffed) can be used as the second alignment layercomprising the same or a different polymer. Additionally, opticalalignment layers can be further processed by conventional alignmenttechniques such as mechanical buffing, either before or after theexposure step.

The process of this invention can be used to make a novel liquid crystaldisplay element, also of this invention. The liquid crystal displayelement of the present invention is composed of an electrode substratehaving at least one optical alignment layer of the present invention, avoltage-impressing means and a liquid crystal material.

FIG. 1 illustrates a typical liquid crystal display element, comprisinga transparent electrode 2 of ITO (indium-tin oxide) or tin oxide on asubstrate 1 and optical alignment layers 3, of the present invention,formed thereon. The optical alignment layers are exposed to polarizedlight of a wavelength or wavelengths within the absorption band of theanisotropically absorbing molecules. A spacer concurrently with asealing resin 4 is intervened between a pair of optical alignment layers3. A liquid crystal 5 is applied by capillary filling of the cell andthe cell is sealed to construct a liquid crystal display element.Substrate 1 may comprise an overcoat film such as an insulating film, acolor filter, a color filter overcoat, a laminated polarizing film etc.These coatings and films are all considered part of the substrate 1.Further, active elements such as thin film transitors, a nonlinearresistant element, etc. may also be formed on the substrate 1. Theseelectrodes, undercoats, overcoats, etc. are conventional constituentsfor liquid crystal display elements and are usable in the displayelements of this invention. Using the thus formed electrode substrate, aliquid crystal display cell is prepared, and a liquid crystal substranceis filled in the space of the cell, to prepare a liquid crystal displayelement in combination with a voltage-impressing means.

The exposed anisotropically absorbing molecules induce alignment of aliquid crystal medium at an angle + and -θ with respect to the directionof the polarization of the incident light beam and along the plane ofthe optical alignment layer. In addition, in the presence of thehydrophobic moieties, the exposed anisotropically absorbing moleculesinduce a pre-tilt at an angle Φ with respect to the plane of the opticalalignment layer.

One skilled in the art will recognize that the process of the instantinvention allows control of the alignment of a liquid crystal medium inany desired direction within the plane of the optical alignment layer bycontrolling the conditions of the polarized light exposure. Preferrablythe liquid crystal medium is aligned at an angle + and -θ, where θ isequal to 90° with respect to the direction of polarization.

Pre-tilt is an important feature in the operating performance of mostliquid crystal displays. FIG. 2 illustrates the pre-tilt angle Φ. Theliquid crystal director, 6, is the direction the liquid crystalmolecules adjacent the optical alignment layer 3 orient. "Pre-tilt"refers to the angle the liquid crystal director 6 makes relative to theoptical alignment layer 3, in a plane defined by the normal to thesubstrate and the projection of the local liquid crystal director ontothe alignment layer. As depicted in FIG. 2, the pretilt angle, Φ, canrange from 0° to 180°. Only one substrate is drawn for clarity. For theΦ angles 0° or 180°, the alignment is referred to as homogeneous orplanar alignment. For the Φ angle 90°, the alignment is referred to ashometropic or vertical alignment. For the Φ angle ranges greater than 0°and less than or equal to 45° and less than 180° and greater than orequal to 135°, the alignment is referred to as predominately homogeneousor planar alignment. For the Φ angle range greater than 45° but lessthan 135° exclusive of 90° is referred to as predominately hometropic orvertical alignment.

One skilled in the art will recognize that 0° to 90° pre-tilt isequivalent in magnitude to 180° to 90° pre-tilt, but with opposingdirections. Preferred pre-tilts in the process are in the range of 1° to30° and 179° to 150°. Most preferred pre-tilts are in the range of 2° to15° and 178° to 165°.

A common way to assess pre-tilt is by direct measurement of the pre-tiltin a planar aligned or twisted nematic cell using the crystal rotationmethod of Baur, et al., Phys. Lett., (1976) 56A, 142. This methodassumes that the pre-tilt throughout the thickness of the liquid crystallayer is a constant. Thus it gives an average value of pre-tilt. Thoseskilled in the art know that this measurement technique requiresconstruction of anti-parallel planar or non-splay twisted nematic cellsto insure a uniform pre-tilt throughout the thickness of the cell. Inthe examples that follow twisted nematic cells with a non-splayconfiguration of the alignment layers is used to assess pre-tilt angle.

This invention is demonstrated in the following examples, which areillustrative and not intended to be limiting. The examples of theinvention use several hydrophobic diamines that were prepared bysynthesis.

Hydrophobic diamine 10 was made by the following procedure:

A mixture of 2,4-dinitrophenol (85 wt %, 6.72 g, 31 mmol), octadecylbromide (20.7 g, 62 mmol), sodium carbonate (6.57 g, 62 mmol) anddimethylformamide (31 mL) was heated to 100° C. under a nitrogenatmosphere for 22 h. The cooled mixture was diluted with water (200 mL),acidified with 10N hydrochloric acid (50 mL) and extracted with ether.The extracts were washed with water and brine, and dried over magnesiumsulfate. The solvent was removed and the solid recrystallized to give1-octadecyloxy-2,4-dinitrobenzene (10.7 g, 79%): mp 63.5°-64.0° C.

A mixture of 1-octadecyloxy-2,4-dinitrobenzene (3.99 g 9.15 mmol),tin(II) chloride dihydrate (23.93 g 106 mmol) and absolute ethanol (40mL) was heated to 70° C. for 5 h. The cooled reaction mixture was pouredinto ice and basified with concentrated sodium bicarbonate aqueoussolution. The mixture was extracted with diethyl ether and the extractdried over magnesium sulfate. The solvent was removed and the productpurified by chromatography (silica gel) to give diamine 10 (0.58 g 17%):mp 82.1°-83.0° C.

Hydrophobic diamine 12 was prepared by the following procedure:

A mixture of 1-octadecyloxy-2,5-dinitrobenzene (6.87 g, 15.7 mmol),tin(II) chloride dihydrate (35.5 g, 157.3 mmol) and absolute ethanol (70mL) was heated to 70° C. for 5 h. The cooled reaction mixture was pouredinto ice and basified with concentrated potassium hydroxide aqueoussolution. The mixture was extracted with diethyl ether and the extractdried over magnesium sulfate. The solvent was removed and the productpurified by chromatography (silica gel) to give diamine 12 (5.2 g, 88%):mp 74.0°-74.5° C.

Hydrophobic diamine 16 was prepared by the following procedure:

A mixture of 1-chloro-2,4-dinitrobenzene (Aldrich, 2.02 g, 10 mmol),sodium carbonate (1.27 g, 12 mmol), dioctadecylamine (Pfaltz & Bauer,6.26 g, 12 mmol) and dry dimethylformamide (10 mL) was heated to 80°-90°C. under a nitrogen atmosphere for 1 h. The cooled mixture was dilutedwith water and extracted with ether. The extracts were washed with waterand dried over magnesium sulfate. The solvent was removed and the solidrecrystallized to give N,N-dioctadecyl-2,4-dinitrobenzenamine (6.0 g,87%): mp 55.5°-57.5° C.

A mixture of N,N-dioctadecyl-2,4-dinitrobenzenamine (11.8 g 17.2 mmol),5% palladium on carbon (1.8 g, 50% water wet) and tetrahydrofuran (180g) was hydrogenated at 55 psi and room temperature in a Parr shaker for7 h. The mixture was filtered through celite and the solvent removed togive a solid. The solid was recrystallized from ethanol to give diamine16 (7.47 g, 68%): mp 41.5°-44.0° C.

EXAMPLE 1

This example illustrates the process of inducing pre-tilt in alignmentof a liquid crystal medium with a novel composition of the invention.

To a solution of 4,4'-diaminobenzophenone (100.8 mg, 0.475 mmol) and4-(1H, 1H-pentadecafluoro-1-octyloxy)-1,3-benzenediamine, 8, (12.7 mg,0.025 mmol) in γ-butyrolactone (1.39 g) was added5-(2,5-dioxotetrahydro)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, D3, (132.1 mg, 0.5 mmol) all at once. The mixture was stirredunder a nitrogen atmosphere at room temperature for 16 h. A solution ofacetic anhydride (0.142 mL, 1.5 mmol) in γ-butyrolactone (1.0 g) andtriethylamine (0.21 mL, 1.5 mmol) were added, consecutively, and thesolution heated to 120° C. for 3 h. The solution was cooled and dilutedto 3 wt % with γ-butyrolactone (5.44 g) to give a polymer solution readyfor spin casting.

Two 0.9 inch by 1.2 inch by 1 millimeter thick borosilicate glasssubstrates with transparent indium-tin-oxide (ITO) electrode coatings(Donnelly Corp., Holland, Mich.) were spin-coated and cured with thepolyimide formulation to give optical alignment layers. Spin coating wasachieved by filtering the above solution through an 0.45 μm Teflonfilter membrane directly onto the surface of the clean ITO glasssubstrates. The coated ITO glass substrates were then spun at 2500 RPMfor 1 min to produce uniform thin films. The resultant thin films werecured under nitrogen 0.25 h at 80° C. followed by 1 h at 180° C.

The coated substrates were exposed to ultrviolet polarized light usingthe set-up schematically represented in FIG. 3. In this experiment eachcoated substrate 7 was mounted onto a 2-axis XY translation stage(indicated by double-headed arrows 8 in FIG. 3) with the coated sidesfacing the incident laser beam. An Innova 400 (Coherent Incorporated,Santa Clara, Calif.) laser 9 was tuned to lase in the ultraviolet withwavelengths ranging from 308 to 336 nm. A mirror 11 directs the light toa 5 cm focal length cylindrical lens 12 which focused the incident 1 cmbeam to a line (1 cm×200 μm) onto each coated substrate 7. The coatedsubstrate was translated at a 3.0 mm/s constant speed along the Ydirection and then stepped in the X direction. This was repeated untilthe coated substrate had been completely exposed. The incident opticalpower was 0.25 Watts and the ultraviolet light was polarized along 10.

A twisted nematic liquid crystal cell was constructed from the twoexposed coated substrates. Six micron glass fiber spacers (EMIndustries, Inc., Hawthorne, N.Y.) were mixed in with an epoxy and theepoxy mixture was placed at the edges of the coated side on one exposedsubstrate. The second exposed substrate was placed on top of the firstsubstrate such that the alignment layers were facing each other and therespective background alignment directions were perpendicular to eachother. The substrates were pressed to a six micrometer spacing usingclamps and the fiber spacer/epoxy mixture was cured for 5 mins. Twospaces on opposite sides of the cell were left unsealed so that theliquid crystal will fill the cell along the bisector between thealignment directions of the substrates. The cell was placed in a vacuumand, subsequently, one unsealed opening on the cell was dipped intoZLI4792 nematic liquid crystal (EM Industries, Inc., Hawthorne, N.Y.)doped with 0.1% ZLI811 (EM Industries, Inc., Hawthorne, N.Y.) chiralcompound. After filling, the cell was removed from the liquid crystaland vacuum, cleaned up, and the spaces sealed with epoxy.

The cell was viewed between parallel and crossed polarizers on aphotographic light box. For the two polarizer configurations, thetransmission of the cell was consistent with a twisted nematicorientation of the liquid crystal and the majority of the cell gave anet uniform twisted nematic alignment. The pretilt angle was measured,using the crystal rotation method, to be approximately 8 degrees.

EXAMPLE 2

To a solution of 4,4'-diaminobenzophenone (95.5 mg, 0.45 mmol) anddiamine 8 (25.3 mg, 0.05 mmol) in γ-butyrolactone (1.43 g) was addeddianhydride D3 (132.1 mg, 0.5 mmol) all at once. The mixture was stirredunder a nitrogen atmosphere at room temperature for 16 h. A solution ofacetic anhydride (0.142 mL, 1.5 mmol) in γ-butyrolactone (1.0 g) andtriethylamine (0.21 mL, 1.5 mmol) were added, consecutively, and thesolution heated to 120° C. for 3 h. The solution was cooled and dilutedto 3 wt % with γ-butyrolactone (5.44 g) to give a polymer solution.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 with a scan speed of 0.5 mm/s. The results werethe same as Example 1 except that the pretilt was measured to beapproximately 18 degrees.

EXAMPLE 3

To a solution of 2-(trifluoromethyl)-1,4-benzenediamine, 1, (44.0 mg,0.25 mmol), 3,3'-bis(trifluoromethyl)benzidene, 5, (40.0 mg, 0.125 mmol)and diamine 8 (63.3 mg, 0.125 mmol) in γ-butyrolactone (2.0 g) was added3,3',4,4'-benzophenonetetracarboxylic dianhydride, D1, (161.1 mg, 0.5mmol) all at once. The mixture was stirred under a nitrogen atmosphereat room temperature for 16 h. A solution of acetic anhydride (0.142 mL,1.5 mmol) in γ-butyrolactone (1.0 g) and triethylamine (0.21 mL, 1.5mmol) were added, consecutively, and the solution heated to 120° C. for3 h. The solution was cooled and diluted to 3 wt % with -butyrolactone(6.67 g) to give a solution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the coated substrates were glass withoutITO (Donnelly Corp., Holland, Mich.). The results were the same asExample 1 except that scan speed was 0.5 mm/s and the pretilt wasmeasured to be approximately 31 degrees.

EXAMPLE 4

To a solution of 4,4'-diaminobenzophenone (95.5 mg, 0.45 mmol) anddiamine 8 (25.3 mg, 0.05 mmol) in γ-butyrolactone (1.75 g) was addeddianhydride D1 (161.1 mg, 0.5 mmol) all at once. The mixture was stirredunder a nitrogen atmosphere at room temperature for 16 h. The solutionwas diluted to 3 wt % with γ-butyrolactone (7.37 g) to give a polymersolution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the liquid crystal used was MLC6043-000(EM Industries, Inc., Hawthorne, N.Y.) with 0.1% ZLI811, and the scanspeed was 1.5 mm/s. The results were the same as Example 1 except thatthe pretilt was measured to be approximately 10 degrees.

EXAMPLE 5

To a solution of 4,4'-diaminobenzophenone (95.5 mg, 0.45 mmol) anddiamine 8 (25.3 mg, 0.05 mmol) in γ-butyrolactone (1.25 g) was added1,2,3,4-butanetetracarboxylic dianhydride, D7, (99.0 mg, 0.5 mmol) allat once. The mixture was stirred under a nitrogen atmosphere at roomtemperature for 16 h. A solution of acetic anhydride (0.142 mL, 1.5mmol) in γ-butyrolactone (1.0 g) and triethylamine (0.21 mL, 1.5 mmol)were added, consecutively, and the solution heated to 120° C. for 3 h.The solution was cooled and diluted to 3 wt % with γ-butyrolactone (4.55g) to give a polymer solution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the scan speed was 0.5 mm/s. The resultswere the same as Example 1 except that the pretilt was measured to beapproximately 20 degrees.

EXAMPLE 6

To a solution of 4,4'-diaminobenzophenone (100.8 mg, 0.475 mmol) anddiamine 8 (12.7 mg, 0.025 mmol) in γ-butyrolactone (1.20 g) was addeddianhydride D7 (99.0 mg, 0.5 mmol) all at once. The mixture was stirredunder a nitrogen atmosphere at room temperature for 16 h. A solution ofacetic anhydride (0.142 mL, 1.5 mmol) in γ-butyrolactone (1.0 g) andtriethylamine (0.21 mL, 1.5 mmol) were added, consecutively, and thesolution heated to 120° C. for 3 h. The solution was cooled and dilutedto 4 wt % with γ-butyrolactone (2.59 g) to give a polymer solution readyfor spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the scan speed was 1.5 mm/s. The resultswere the same as Example 1 except that the pretilt was measured to beapproximately 22 degrees.

EXAMPLE 7

To a solution of diamine 1, (83.6 mg, 0.475 mmol) and diamine 8 (12.7mg, 0.025 mmol) in γ-butyrolactone (1.46 g) was added dianhydride D1(161.1 mg, 0.5 mmol) all at once. The mixture was stirred under anitrogen atmosphere at room temperature for 16 h. The solution wasdiluted to 4 wt % with γ-butyrolactone (4.72 g) to give a polymersolution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the scan speed was 5 mm/s. The resultswere the same as Example 1 except that the pretilt was measured to beapproximately 8 degrees.

EXAMPLE 8

To a solution of 5-(trifluoromethyl)-1,3-benzenediamine, 2, (66.0 mg,0.375 mmol), and diamine 8 (63.3 mg, 0.125 mmol) in γ-butyrolactone(1.46 g) was added dianhydride D1 (120.8 mg, 0.375 mmol) and dianhydrideD3 (33.0 mg, 0.125 mmol) all at once. The mixture was stirred under anitrogen atmosphere at room temperature for 16 h. The solution wasdiluted to 4 wt % with γ-butyrolactone (5.19 g) to give a polymersolution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the scan speed was 0.25 mm/s. The resultswere the same as Example 1 except that the pretilt was measured to beapproximately 10 degrees.

EXAMPLE 9

To a solution of 4,4'-diaminobenzophenone (79.6 mg, 0.375 mmol) anddiamine 10, (47.0 mg, 0.125 mmol) in γ-butyrolactone (1.92 g) was addeddianhydride D1 (161.1 mg, 0.5 mmol) all at once. The mixture was stirredunder a nitrogen atmosphere at room temperature for 16 h. A solution ofacetic anhydride (0.142 mL, 1.5 mmol) in γ-butyrolactone (1.0 g) andtriethylamine (0.21 mL, 1.5 mmol) were added, consecutively, and thesolution heated to 120° C. for 3 h. The solution was cooled and dilutedto 4 wt % with γ-butyrolactone (4.98 g) to give a polymer solution readyfor spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the scan speed was 1.5 mm/s. A pretilt>1degree was observed by the crystal rotation method.

EXAMPLE 10

To a solution of 4-(1H, 1H,11H-eicosafluoro-1-undecyloxy)-1,3-benzenediamine, 9, (39.9 mg, 0.0625mmol) and 4,4'-diaminostilbene (13.1 mg, 0.0625 mmol) inN-methylpyrolidone (NMP) (0.89 g) was added dianhydride D1 (40.25 mg,0.125 mmol) dissolved in NMP (0.89 g). The mixture was stirred for 17 hat room temperature under a nitrogen atmosphere. The mixture was dilutedwith 1 wt % solids with anhydrous tetrahydrofuran (THF) (7.15 g) to givea polymer solution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the coated substrates were glass withoutITO and the scan speed was 1.5 mm/s. The results were the same asExample 1 except that the pretilt was measured to be approximately 23degrees.

EXAMPLE 11

To a solution of 1,3,4-(N,N-dioctadecyl)benzenetriamine, 16, (39.2 mg,0.0625 mmol) and 4,4'-diaminostilbene (13.1 mg, 0.0625 mmol) in NMP(0.88 g) was added a solution of dianhydride D1 (40.2 mg, 0.125 mmol) inNMP (0.88 g).The mixture was stirred for 18 h at room temperature undera nitrogen atmosphere. The mixture was diluted with 1 wt % solids withanhydrous tetrahydrofuran (THF) (6.65 g) to give a polymer solutionready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the coated substrates were glass withoutITO and the scan speed was 1.5 mm/s. The results were the same asExample 1 except that the pretilt was measured to be approximately 28degrees.

EXAMPLE 12

3-Trifluoromethyl-4-(3'-trifluoromethyl-4'-aminophenyl)azobenzenamine,C, was first prepared using the following procedures:

2-Trifluoromethyl-4-nitro-benzeneamine (4.92 g, 23.8 mmol) slurried in5N hydrochloric acid (15.8 mL) and ice (16 g) was diazotized with 2Msodium nitrite (12.6 mL, 25 mmol) at 0°-5° C., followed by coupling with3-trifluoromethylbenzeneamine (5.0 g, 31 mmol) in 5N hydrochloric acid(8 mL) at 0°-5° C. The mixture was stirred occasionally for 0.5 h,basified with 25 wt % aqueous potassium carbonate. The resulting solidwas recrystallized from THF-ethanol (1:1) to give4-(3'-trifluoromethyl-4'-nitrophenyl)azobenzeneamine: 1.8 g; mp144.0°-145.5° C.

The above monoazo nitroamine (1.65 g, 4.36 mmol) in ethanol (20 mL) wastreated with a solution of sodium sulfide nonahydrate (2.1 g, 8.7 mmol)in water (2 mL). The mixture was heated to 80° C. for 0.5 h, followed byaddition of a similar amount of sodium sulfide nonahydrate solution. Themixture was heated for 1 h and diluted with water (200 mL). Theresulting solid was dissolved in hot ethanol and filtered and theethanol removed to give3-trifluoromethyl-4-(3'-trifluoromethyl-4'-aminophenyl)azobenzena; mp135.5°-136.5° C.

To a solution of diamine 8 (31.6 mg, 0.0625 mmol) and3-trifluoromethyl-4-(3'-trifluoromethyl-4'-aminophenyl)azobenzenamine,C, (21.7 mg, 0.0625 mmol) in NMP (0.89 g) was added a solution ofdianhydride D1 (40.2 mg, 0.125 mmol) in NMP (0.89 g). The mixture wasstirred under a nitrogen atmosphere for 18 h at room temperature. Themixture was diluted with 1 wt % solids with anhydrous tetrahydrofuran(THF) (7.49 g) to give a polymer solution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the coated substrates were glass withoutITO and the scan speed was 1.5 mm/s. The results were the same asExample 1 except that the pretilt was measured to be approximately 40degrees.

EXAMPLE 13

This example demonstrates that the polyimide of Example 1 can opticallyinduce the alignment of liquid crystals when exposed to polarizedultraviolet lamp light.

Two coated substrates 7 coated with the polyimide of Example 1 wereexposed by an ultraviolet lamp as depicted in FIG. 4. The ultravioletlamp 13 (UV Process Supply, Chicago, Ill., Model Porta-Cure 1500F) was16 cm from the substrates 7 with the coated side facing the lamp. A 3×4inch dielectric polarizer 14 (CVI Laser Corporation, Albuquerque, N.Mex.) was placed in front of the light beam. The polarizer 14 gaveapproximately 20:1 of p-polarized light 15 to s-polarized light intransmission for wavelengths between 300-400 nm. The light wassubsequently passed through a 1 mm thick soda lime glass plate 16(Donnelly Mirrors, Inc., Holland, Mich.). The glass plate 16 has acut-off of approximately 300 nm (transmission is less than 10% for anywavelength less than 300 nm). To prevent illumination of the coatedsubstrates 7 from unpolarized stray light, aluminum foil (not shown infigure) was placed to block all light that did not pass through thepolarizer 14. The output of the lamp 13 was set at 200 Watts/inch andallowed to warm-up for 10 minutes prior to placing the coated substrates7 in front of the light beam.

The power density of the light beam at the substrates 7 was measured tobe 14 milliwatts/cm² using a Control Cure compact radiometer from UVProcess Supply, Chicago, Ill. The substrates were exposed for 10 minutesand a cell was assembled and filled as in Example 1.

The results were the same as in Example 1. A pretilt>1 degree wasobserved by the crystal rotation method.

EXAMPLE 14

To a solution of diamine 1 (79.2 mg, 0.45 mmol) and diamine 8 (25.3 mg,0.05 mmol) in γ-butyrolactone (1.84 g) was added dianhydride D1 (161.1mg, 0.5 mmol) all at once. The mixture was stirred under a nitrogenatmosphere at room temperature for 16 h. The solution was diluted to 4wt % with γ-butyrolactone (4.53 g), filtered through a 0.45 μm teflonfilter and spin coated onto soda-lime glass substrates (0.9"×1.2") at2500 rpms. The coated substrates were dried at 80° C. for 0.25 h and180° C. for 1 h in a nitrogen atmosphere and stored in a nitrogenatmosphere at room temperature until used.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the scan speed was 0.5 mm/s. The resultswere the same as Example 1 except that the pretilt was measured to beapproximately 17 degrees.

EXAMPLE 15

To a solution of 4,4'-diaminobenzophenone (79.6 mg, 0.375 mmol) anddiamine 12, (47.0 mg, 0.125 mmol) in γ-butyrolactone (1.63 g) was addeddianhydride D1 (161.1 mg, 0.5 mmol) all at once. The mixture was stirredunder a nitrogen atmosphere at room temperature for 16 h. The solutionwas diluted to 4 wt % with γ-butyrolactone (5.27 g) to give a polymersolution ready for spin casting.

The polymer solution was spin coated, cured and optically processed asdescribed in Example 1 except the scan speed was 1.5 mm/s. The resultswere the same as Example 1 except that the pretilt was measured to be<1.0 degree.

If the liquid crystal displays prepared according to each of the aboveExamples, after optically inducing pre-tilt, are visually examined under100× magnification between crossed polarizers, these liquid crystaldisplays will exhibit substantially no irregularities in the pattern ofalignment resulting

                  TABLE 1    ______________________________________    Dye    Designation            Structure    ______________________________________             ##STR15##    B             ##STR16##    C             ##STR17##    ______________________________________

                  TABLE 2    ______________________________________    No.     Structure    ______________________________________    Diamines used in Polyimide Alignment Layers             ##STR18##    2             ##STR19##    3             ##STR20##    4             ##STR21##    5             ##STR22##    6             ##STR23##    Diamines used in Polyimide Optical Alignment Layers    7             ##STR24##    8             ##STR25##    9             ##STR26##    10             ##STR27##    11             ##STR28##    12             ##STR29##    Diamines used in Polyimide Alignment Layers    13             ##STR30##    14             ##STR31##    15             ##STR32##    16             ##STR33##    ______________________________________

                  TABLE 3    ______________________________________    Alicyclic tetracarboxylic dianhydrides    No.  Structure    ______________________________________    D3          ##STR34##    D4          ##STR35##    D5          ##STR36##    D6          ##STR37##    D7          ##STR38##    D8          ##STR39##    D9          ##STR40##    D10          ##STR41##    D11          ##STR42##    ______________________________________

from scratches, while liquid crystal display elements treated bymechanical buffing will exhibit substantial irregularities.

We claim:
 1. A process for inducing pre-tilt in alignment of a liquidcrystal medium adjacent to a surface of an optical alignment layercomprising:(a) exposing at least one optical alignment layer, comprisinganisotropically absorbing molecules and hydrophobic moieties, topolarized light; the polarized light having a wavelength within theabsorption band of said anisotropically absorbing molecules; wherein theexposed anisotropically absorbing molecules induce alignment of theliquid crystal medium at an angle + and -θ with respect to the directionof the polarization of the incident light beam and along the surface ofthe optical alignment layer, and induce a pre-tilt at an angle Φ withrespect to the surface of the optical alignment layer; and (b) applyinga liquid crystal medium to the optical alignment layer.
 2. A process ofclaim 1 wherein the anisotropically absorbing molecules and hydrophobicmoieties are covalently bonded to a polymer.
 3. A process of claim 1wherein the anisotropically absorbing molecules are nonbonded solutesdissolved in a hydrophobic polymer.
 4. A process of claim 2 wherein thepolymer comprises a polyimide polymer.
 5. A process of claim 4 whereinthe polyimide polymer is a reaction product of at least onetetracarboxylic dianhydride and at least one hydrophobic diamine, whichcomprises at least one structural element of the formula I ##STR43##wherein Y is a divalent radical selected from the formulas II and III##STR44## wherein Z is selected from the group consisting of --S--,--O--, --SO₂ --, --CH₂ --,--C(CF₃)₂ --, --C(O)--, --CH₂ CH₂ --, --NR--and a covalent bond wherein R is a C₁ -C₄ hydrocarbon chain; X isindependently selected from R₁, --O--R₁, --S--R₁, --N(R₂)--R₁ ; whereinR₁ is independently selected from C₄ -C₂₀ perfluorinated alkyl chain, C₄-C₂₀ partially fluorinated alkyl chain, and C₁ -C₂₀ hydrocarbon chain;X₁ is independently selected from X and H; R₂ is independently selectedfrom H, C₁ -C₉ hydrocarbon chain and and R₁ ; and wherein M is atetravalent organic radical derived from said tetracarboxylicdianhydride containing at least two carbon atoms, no more than twocarbonyl groups of the dianhydride being attached to any one carbon atomof the tetravalent radical.
 6. A process of claim 5 wherein thepolyimide polymer is a copolyimide which additionally comprises at leastone structural element offormula Ia ##STR45## wherein Y₁ is a divalentorganic radical having at least two carbon atoms other than Y; M is asdefined in claim 5; and wherein the ratio of structural elements offromula I and Ia are 1:99 to 99:1.
 7. A process of claim 5 wherein thetetracarboxylic dianhydride is a diaryl ketone tetracarboxylicdianhydride and said structural element of the formula I is formula IV##STR46## wherein X₂ is independently selected from the group consistingof H, CL, F, Br, R₃ and R₃ O--, wherein R₃ is independently selectedfrom C₁ -C₃ perflourinated alkyl chain, C₁ -C₃ partially flourinatedalkyl chain and C₁ -C₈ hydrocarbon chain; m is 1 or 0; and Z and Y areas defined in claim
 5. 8. A process of claim 5 wherein at least onetetracarboxylic dianhydride is an alicyclic tetracarboxylic dianhydride.9. A process of claim 7 wherein the polyimide polymer is a copolymer,and additionally includes an alicyclic tetracarboxylic dianhydride,which further comprises the structural element of formula V ##STR47##wherein P is a tetravalent organic radical derived from said alicyclictetracarboxylic dianhydride containing at least four carbon atoms, nomore than one carbonyl group of the dianhydride being attached to anyone carbon atom of the tetravalent radical; Y is as defined in claim 5.10. A process of claim 9 wherein the copolymer comprises a ratio ofstructural elements of formulas IV and V of 1:10 to 99:1.
 11. A processof claim 9 wherein the alicyclic tetracarboxylic dianhydride is selectedfrom 5-(2,5-dioxotetrahydro)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, 2,3,5-tricarboxycyclopentaneacetic acid dianhydride,1,2,3,4-butanetetracarboxylic acid dianhydride andcyclobutanetetracarboxylic acid dianhydride.
 12. A process of claim 7wherein the diaryl ketone tetracarboxylic anhydride is3,3',4,4'-benzophenonetetracarboxylic dianhydride.
 13. A process ofclaim 5 wherein the polyimide polymer is a copolyimide whichadditionally comprises at least one structural element of formula VI##STR48## wherein X₂ is independently selected from the group consistingof H, CL, F, Br, R₃ and R₃ O--, wherein R₃ is independently selectedfrom C₁ -C₃ perflourinated alkyl chain, C₁ -C₃ partially flourinatedalkyl chain and C₁ -C₈ hydrocarbon chain; and M is as described in claim5.
 14. A process of claim 5 wherein the hydrophobic diamine is selectedfrom the group consisting of4-(1H,1H-pentadecafluoro-1-octyloxy)-1,3-benzenediamine,4-(1H,1H,11H-eicosafluoro-1 -undecyloxy)-1,3-benzenediamine,4-(1-octadecyloxy)-1,3-benzenediamine,4-(1-hexadecyl)-1,3-benzenediamine and2-(1-octadecyloxy)-1,4-benzenediamine.
 15. A process of claim 1 whereinthe anisotropically absorbing molecules are selected from the grouparylazo, poly(arylazo), stilbene and diaryl ketone derivatives.
 16. Aprocess of claim 1 wherein the anisotropically absorbing molecules areselected from the group arylazo, stilbene and diaryl ketone derivativeshaving absorbance maxima between 150 and 400 nm.
 17. A process of claim1 wherein the anisotropically absorbing molecules are selected from thegroup consisting of 4,4'-diaminostilbene, the2,4-diaminophenylhydrazones of benzophenone, 4,4'-diaminobenzophenone,and 3,3'-bis(trifluoromethyl)benzophenone and diazodiamine A.
 18. Aprocess of claim 1 wherein the anisotropically absorbing molecules areselected from the group consisting of benzophenone,4,4'-bis(trifluoromethyl)benzophenone,3,4'-bis(trifluoromethyl)benzophenone,3,3'-bis(trifluoromethyl)benzophenone; and phenylhydrazones ofbenzophenone, 4,4'-bis(trifluoromethyl)benzophenone,3,4'-bis(trifluoromethyl)benzophenone; and3,3'-bis(trifluoromethyl)benzophenone.
 19. A process of claim 1 whereinthe polarized light is from a laser.
 20. A process of claim 1 whereinthe polarized light is from a source selected from the group: mercuryarc, xenon deuterium, and quartz tungsten halogen lamp, and blacklights; in combination with a polarizer.
 21. A process of claim 1wherein the exposing is performed in a scanning mode.
 22. A process ofclaim 1 wherein the exposing comprises delivery of 0.001 to 2000 J/cm²,within the absorption band of the anisotropically absorbing molecules,to said optical alignment layer.
 23. A process of claim 1 wherein theexposing is a two step process of:(a) exposing at least one opticalalignment layer to polarized light at a normal incidence, and (b)exposing said optical alignment layer to polarized light at an obliqueincidence.
 24. A process of claim 1 wherein said exposing is a two stepprocess of:(a) exposing said optical alignment layer to polarized lightof a first direction of linear polarization of the incident light, and(b) exposing said optical alignment layer to polarized light of a seconddirection of linear polarization of the incident light.
 25. A process ofclaim 1 wherein the exposing is a two step process of:(a) exposing saidoptical alignment layer to polarized light of a first direction oflinear polarization of the incident light, and (b) exposing said opticalalignment layer to polarized light of second direction of linearpolarization of the incident light, at an oblique incidence.
 26. Aprocess of claim 1 wherein the polarized light has one or morewavelengths of about from 150 to 800 nm.
 27. A process of claim 1wherein the polarized light has one or more wavelengths of about from150 to 400 nm.
 28. A process of claim 1 wherein the polarized light hasone or more wavelengths of about from 300 to 400 nm.
 29. A process ofclaim 1 wherein the applying a liquid crystal medium comprises capillaryfilling a cell.
 30. A process of claim 1 wherein the applying a liquidcrystal medium comprises casting of said liquid crystal medium onto anoptical alignment layer.
 31. A process of claim 1 wherein the liquidcrystal medium is selected from the group consisting of nematic liquidcrystals, ferroelectric liquid crystals, polymerizable nematic liquidcrystals and nematic liquid crystalline polymers.
 32. A process of claim1 wherein the liquid crystal medium is selected from the groupconsisting of nematic liquid crystals and polymerizable nematic liquidcrystals.
 33. A process of claim 32 wherein the nematic liquid crystalsare selected from the group consisting of 4-cyano-4'-alkylbiphenyls,4-alkyl-(4'-cyanophenyl)cyclohexanes and superflourinated liquid crystalmixtures.
 34. A process of claim 1 wherein the alignment of the liquidcrystal medium is at an angle + and -θ, wherein θ is equal to 90°.
 35. Aprocess of claim 1 wherein the pre-tilt at an angle Φ is about from 1°to 30°.
 36. A process of claim 1 wherein the pre-tilt at an angle Φ isabout from 2° to 15°.
 37. A liquid crystal display element derived fromprocess of claim 1.